(i) Field of the Invention
This invention relates to a milk coagulating enzyme for the making of cheese, and to a method for its extraction.
(ii) Description of the Prior Art
Rennet, the traditional milk coagulating enzyme used for manufacturing cheese, is obtained from calf stomach, which at present is of limited supply. Therefore rennet is very costly. Consequently, milk coagulating enzymes from swine, chicken and adult bovine stomachs and also those from bacteria and fungi are used as rennet substitutes.
Rennet from calf stomachs have some unique characteristics which are missing in the substitutes. Consequently there are reports (e.g. in chapter 12 entitled "Milk Clotting Enzymes and Cheese Chemistry, Part 1. Milk-Clotting Enzymes and their Action, by C. A. Ernstrom et al in "Fundamentals of Dairy Chemistry" Second Edition, the Avi Publishing Company Inc. Westport Conn. 1974) that use of these substitutes results in cheeses of inferior quality and poorer yield. Thus, it was reported that most plant proteases are strongly proteolytic and cause extensive digestion of the curd. This has resulted in reduced yields, bitter flavors and pasty-bodied cheese. Patents have been issued for the production of and use of milk-clotting enzymes from bacteria, e.g. Godo Shusei Co., Japanese Pat. Nos. 27,714.69 (1969) and 12,225/70 (1970) and British Pat. Nos. 1156387 and 1156388 (1969); John Labatt Ltd., British Pat. Nos. 1,202,378 (1970), 1203371 (1970) and 1223860 (1971); and Murray et al, U.S. Pat. No. 3,543,563 (1970) and 3,507,750 (1970). However, results have not been consistently favorable. Patents have also been issued for the production of milk-clotting enzymes from fungi, e.g. Arima et al, U.S. Pat. No. 3,212,905 (1965), and W. German patent application No. 1,442,118 (1969); Aunstrup, W. German patent application No. 151,775 (1970); Charles et al, U.S. Pat. No. 3,549,390 (1970) and W. German patent application No. 1945447 (1970); and Sardinas, U.S. Pat. No. 3,275,453 (1966) and W. German patent application No. 1,442,140 (1968). In addition porcine pepsin and bovine pepsin have been investigated for their milk-clotting potential. For harder varieties of cheese, e.g., cheddar, which is the most popular in North America, these substitutes often need to be blended with calf rennet. Therefore, there is still considerable demand for a milk-clotting enzyme with characteristics closely resembling those of calf rennet.